1. Field of the Invention
This invention relates to a process for increasing the wear life of ceramic dies and other ceramic parts used in industrial processing.
2. Description of the Prior Art
Ion implantation is a process for injecting atoms of any element into any solid material to selected depths and concentrations in order to form an alloy or other solid mixture that has a different composition from the original solid. The different composition so formed exhibits different and often highly desirable chemical and physical properties. Encyclopedia of Chemical Technology, Kirk-Othmer, Vol. 13, p. 706 (1981).
By the process of ion implantation, atoms of a selected chemical element are ionized by collisions with electrons in an electrical discharge in a gas at low pressure. These ions pass through an orifice into a high-vacuum region where they are accelerated by an electric field to a moderate energy. The selected ions are then accelerated to the desired energy, refocused by a quadrupole lens, deflected by a scanner system, collimated by a defining aperture, and allowed to strike the target. When the ions penetrate the target lattice, they lose energy through collisions with lattice atoms and come to rest therein. Encyclopedia of Chemical Technology, id.
Metal alloys produced by ion implantation generally have the same corrosion properties as conventional bulk alloys of about the same composition. Moreover, as ion implantation is essentially a brute force (athermal) process involving individual atoms, the process is not restricted by the laws of thermodynamics governing equilibrium processes. For example, the implanted atoms can be placed at any desirable location and to any desired concentration in a solid material (within the limitations of available ion energy) without being restricted by diffusivity constants or solubility constants. Encyclopedia of Chemical Technology, id. Appropriately, ion implantation has been used in the treatment of steels and carbides.
U.S. Pat. No. 3,832,219 illustrates the use of ion implantation in the treatment of stainless and mild steels to modify their surface structure to produce harder or more corrosion resistant surfaces. The ions used are carbon (C), for hardening, and chromium (Cr) for corrosion resistance. Ion energies used are 1-200 KeV.
U.S. Pat. No. 4,105,433 illustrates the use of ion implantation with Co-cemented tungsten carbide (WC) tools. The ions used are Co.sup.+, B.sup.+, N.sup.+, O.sup.+ and Cl.sup.+. By implanting these ions in these tools, reduced adhesion is observed between the Co binder phase in the tool and the metal being treated. The ion dosage or fluence must be greater than 10.sup.17 ions cm.sup.-2 to achieve this effect of reduced adhesion.
Unrelated to ion implantation, but often confused therewith, is ion plating. Ion plating is a coating process which occurs in a glow discharge in a gas at a pressure of a few Pascals, and the energies of the ions and neutral atoms as they strike the surface are from 0.2-1 Kev. In contrast to this, ion implantation does not produce a coating. Moreover, with ion implantation there is no sharp interface between the implanted region and the substrate as there is with ion plating. Encyclopedia of Chemical Industry, id.
U.S. Pat. Nos. 3,915,757 and 3,988,955 illustrate the use of an ion plating technique to plate a metal tool surface to increase the hardness of the tool surface. The increased metal hardness provides tools which have superior cutting power and durability.
The ion-nitriding process disclosed in U.S. Pat. No. 4,194,930 forms a metal nitride on the surface by placing the metal in a discharge of nitrogen and hydrogen gas. This process is a surface coating treatment and not an ion implantation treatment.
U.S. Pat. No. 4,252,626 illustrates the use of ion plating to produce ceramic coatings on other materials. Ions are used to sputter material from a ceramic target. This material then lands on the substrate to be coated, forming a surface film. The ions are not used to modify the ceramic target, but only to sputter material therefrom.
In recent years, the use of ceramic dies and parts has greatly increased. As a class of materials, ceramics are better electrical and thermal insulators and are more stable in chemical and thermal environments than are metals. Moreover, high performance ceramic materials often have greatly improved piezoelectric, magnetic, pyroelectric, electro-optic, laser and mechanical properties. Appropriately, ceramic materials have found use in many new, demanding and highly technical applications.
Not surprisingly, the ceramics industry has devised production and control techniques for mass producing complex shapes in ceramic bodies having carefully controlled electrical, magnetic and/or mechanical properties, while maintaining dimensional tolerances which are good enough to permit relatively easy assembly with other components. Encyclopedia of Chemical Technology, id.
With the extensive use of ceramic dies and other ceramic parts, particularly in highly degradative chemical and thermal environments, it would be very desirable to enhance the wear resistance of these dies and parts. However to date, techniques for improving the wear resistance of ceramic dies and parts have generally involved depositing hard coatings such as titanium nitride on the dies and parts. These techniques have the disadvantage of possible spalling, flaking or cracking, and inevitably, of changing the size of the original part. In such an instance, it is often necessary to manufacture an oversize die or an undersize drill, for example, which can be an expensive undertaking.
Hence, a need continues to exist for a process which increases the wear life of ceramic dies and other ceramic parts wherein the die or part does not suffer from spalling, flaking or cracking and wherein the original dimensional tolerances of the die or part remain unaffected.